1. Field of the Invention
The invention relates to metering syringes and somewhat more particularly to such syringes for transferring fluids in predetermined volumes from one container to another container and being comprised of a piston-burette with a pneumatic drive connected to a valve means in such a manner that the piston burette, the valve means and the pneumatic drive form a unitary structural unit.
2. Prior Art
In instances where a piston-burette is provided with a pneumatic drive, the cylinder of the pneumatic drive is typically attached to the piston-burette. In this combination, the cylinder of the pneumatic drive is attached to the housing of the piston-burette at the drive or output side of the drive. However, significant difficulties arise during assembly of such a unit because the glass cylinder and the piston, which typically is composed of metal, must be aligned exactly. Further, such a unit forms a very long shape, making it cumbersome.
The use of a pneumatic drive to actuate a piston-burette typically requires two valves, one for each direction in which the piston moves. While one side of a piston is under pressure, the other side of the piston must be evacuated. The control of these operations is only possible with so-called multi-path valves. After a piston stroke has been completed, the compressed air is typically switched-off and an operator cannot see, after the shutdown operation, whether the piston is in one or the other operative position. In order to positively prevent possible misconnections, special piston-positioned indicators must be provided. However, such requirement considerably increases the cost of such pneumatically driven piston-burettes.